Recently, considerable effort is being expended to develop wings capable of generating tractive force for the purposes of powering a user on a variety of vehicles that are tethered solely by flexible lines. Such wings can generally be considered kites. The development of kites capable of generating significant force has made possible numerous recreational pursuits. For example, kite surfing or kite boarding refers to a sport involving the use of a wind powered wing to pull the participant on a vehicle across a body of water. Similar sports involving the use of appropriately configured vehicles to traverse sand, earth, snow and ice are also being pursued. One of skill in the art will also recognize that wind powered wings can be used in any number of other applications, whether recreational or practical. With the development of these applications has come an increasing demand for kites having improved characteristics.
One type of kite that has achieved popularity is a leading edge inflatable (“LEI”) kite, typically comprising a semi-rigid framework of inflatable struts or spars that support a canopy to form the profile of the wing. This basic design is taught by U.S. Pat. No. 4,708,078 to Legaignoux, et al. The development of the LEI kite is generally credited with spurring the development of modern kite surfing due to its ability to be relaunched from the water's surface.
Despite the success of LEI kite designs, they do present certain, inherent challenges. As one having skill in the art appreciates, the airfoil presented by the canopy of the kite determines how the kite will perform. Particularly important characteristics include performance, handling, efficiency, relaunchability and power control, most of which are interrelated. Unfortunately, improving one aspect of a given airfoil often degrades performance in other areas. For example, attempts to improve the performance of a kite by increasing the aspect ratio of the wing typically makes the kite more difficult to relaunch. Similarly, one aspect of a kite's efficiency is its lift to drag ratio, but increasing this ratio can have adverse effects on the handling of the kite. Thus, obtaining a desirable balance of characteristics can be difficult.
A related issue is that different characteristics may be desirable for different users or under different conditions. For example, more advanced users may desire a kite with a higher aspect ratio, which can offer greater efficiency but will require more sensitive control and will be more susceptible to changes in wind velocity and direction. In contrast, more novice users often use a kite having lower aspect ratio, which is generally more forgiving to variations in wind and does not demand as precise input from the user. As another example, users looking for the best performance when jumping often seek kites having an airfoil that exhibits high efficiency. On the other hand, users primarily kiting in wave conditions often seek kites that generate relatively constant and uniform power. Given these observations, it would clearly be desirable to utilize a kite having characteristics that could be tuned to fit the conditions or the type of performance desired by the user.
Conventional kites controlled by four lines do offer the ability to tune the kite's performance in one manner. By changing the length of the front lines with respect to the back lines, the user can adjust the angle of attack of the kite's airfoil. However, this type of trim control does not offer any means for controlling the canopy's profile. Thus, these prior art systems do not offer a method for altering the characteristics of the canopy's airfoil.
Yet another aspect of kite design is related to the ability to launch or relaunch the kite. As discussed above, kites having relatively high aspect ratios can be difficult to relaunch. However, the problems associated with relaunching a kite are exacerbated when the kite is used on a relatively low friction surface, such as sand, snow and ice. Indeed, relaunching a conventional four-line kite on snow, regardless of aspect ratio, is extremely difficult and usually requires the use of a fifth line attached to the trailing edge of the kite. Thus, improving the relaunchability of a kite generally either constrains the aspect ratio or requires additional design elements.
Prior art attempts to add design elements to improve the relaunchability of kites have not been completely successful. For example, U.S. Pat. No. 6,659,031 to LeGaignoux describes a bridle arrangement for a four-line kite that is able to apply tension to the trailing edge to aid relaunching. However, the bridle system generally decreases the responsiveness of the kite to turning input. Another attempt is disclosed in WO 03/101824 which uses a stopper arrangement to transmit power to a line attached to the trailing edge. However, the stopper arrangement requires a relatively complex interconnection, which is subject to fouling. Further, both of these prior art methods involve the use of an external line at the trailing edge which can catch on foreign objects, presenting a significant safety problem, and also creates durability and convenience issues while increasing air resistance.
Accordingly, it is an object of the invention to provide a system and method for optimizing the performance of a power kite for different situations and conditions.
It is also an object of the invention to provide a system and method for improving the launchability of a power kite.
It is a further object of the invention to provide a system and method for dynamically controlling the canopy profile.